1. Field of the Invention
The present invention is directed to a method of lengthways sealing and cutting of a foil tube. The foil tube has at least two layers lying on each other and is made of thermoplastic synthetic material. The foil tube is brought to a device suitable for the sealing and cutting in accordance with the present invention.
Additionally, the invention is directed to an apparatus for the sealing and cutting of such a foil tube. The invention has application in that at least one foil tube results into a tube of reduced width.
The invention has application in the production of garbage bags and in the production of bags for the receiving of food, such as thin thermoplastic foils produced in long double-layered tubes.
2. Description of the Prior Art
In prior art processing systems, the layered films are first cut longitudinally and then immediately sealed with each other at the cut edges by heat influence.
The foil tube is brought to a blade over a mostly convex conducting metal. The blade first splits the tube with the edge at the front. The foil is also being heated by means of a seal strip and melts the cut edges of the tube together. The melted edges connect themselves in a lengthways seal seam.
The prior art process is known as a “Slit Seal” procedure. The lengthways seal seam has a characteristic bead of material that increases the overall thickness of the foil by more than 20% of the foil thickness. When winding the tubes manufactured in this manner, the possible diameter of the rolls will be limited by the accumulated diameter of the built up edges, which arises by the Slit Seal procedures. The seam strength moreover decreases particularly with increasing foil thickness.
A further disadvantage is that when the film is guided over a convex plate, electrostatic charges build-up and wrinkles are a likely result. Additionally, during the slit seal procedure, the sealing elements emit considerable heat that needs to be eliminated by an intricate water-cooling system. Finally, the melted foil, as it passes over the convex plate, can create a build up of thermoplastic strings or spiders that require the periodic removal from the plate.